In light of the miniaturization of the semiconductor element, and the high dielectric constant of the barium strontium titanate [hereinafter abbreviated as (Ba,Sr)TiO.sub.3 ] film, the (Ba,Sr)TiO.sub.3 film is used as a dielectric layer of a thin film capacitor of the integrated circuit. The magnitude of the leakage current of the thin film capacitor is directly proportional to the loss of the electric charge that is stored in the thin film capacitor. For this reason, a solution to bring about a reduction in the leakage current of the thin film capacitor is sought by the industry.
The (Ba,Sr)TiO.sub.3 film, which is prepared by sputtering at high temperature or at low temperature preceding a high temperature annealing, exists in the polycrystalline form. When the polycrystalline (Ba,Sr)TiO.sub.3 film is used as the dielectric layer of a thin film capacitor, the thin film capacitor has a tendency to exhibit a relatively large leakage current. In order to inhibit the leakage current, a thicker (Ba,Sr)TiO.sub.3 film may be used. Alternatively, a high temperature oxygen treatment may be carried out in a furnace tube after the formation of the electrodes of the thin film capacitor. However, the sputtering time must be prolonged in the former approach. The latter requires an additional high temperature process.
U.S. Pat. No. 5,471,364 discloses an electrode interface for use together with a material having high dielectric constant. In other words, a buffer layer having a low leakage current density is formed between the electrodes and the high dielectric constant material. In the embodiment of the above disclosure, (Ba,Sr)TiO.sub.3 is used as a high dielectric constant material, whereas SrTiO.sub.3 is used as the buffer layer. Even though the crystalline forms of (Ba,Sr)TiO.sub.3 and SrTiO.sub.3 are not explained in the patent specification, (Ba,Sr)TiO.sub.3 film and SrTiO.sub.3 film, which are formed by the sputtering method, always exist in the polycrystalline form.